Whats up with my XT brakes?

JackHammer
This one?:

that was a very interesting and educational…thanks 😀

@alexh

Yeah I’m leaning towards the worn rotor/pads side of things now.

As far as my understanding of the servowave goes, it allows for wider piston spacing, therefore a bigger gap between pads and rotor so less “shhhhinnngg shhinng” from warped rotors (which was something I always used to get with avids).

This bigger gap is then accommodated for by the “servo” pivot or whatever which instigates more movement at the pistons for the initial lever pull travel (top the bite point).
So it would suggest that this “servo” part of the lever travel is tuned into the width of the rotors and pads, only varying a small amount (ie pad wear). When you add on rotor wear, pad wear and maybe misaligned pistons (not-centered) you get the lever having to go beyond this large movement zone to the “modulation” zone of the lever throw, where there’s comparably little movement of the pistons and a spongey feel on initial pull.

As with the elixir brakes the reservoir on the shimanos may not hold enough fluid to push the pistons out far enough to self adjust to the wider spacing, so require a second pull to get the pistons and lever throw servo tuned bit to bite at the right time.

I am not an engineer so sorry for the terrible technical language.

Rotor and pad wear should have no effect on an open brake system – the whole point is that the pistons move out to compensate for the wear using fluid from the reservoir.

Well, mine have never worked like that. On both bikes, as the pad gets low, the throw to biting increases (it’s slight, but enough to notice when my pads are low).

The only thing I changed on my bike, were the discs. It went from circa 8mm throw (on the lever) to the pads biting, to about 1mm throw.

Get out!

years of happy Avid use here too.

What frustrates me is that shimano don’t seem to be addressing the issue, which is obviously a big one as so many people are suffering the same/similar issues.

I wonder if it really is ‘a big one’ [problem] given the number of Shimano brakes out there and the fact that at least some of the issues seem to be down to user maintenance error? I’m not saying it’s not annoying or unheard of, just that it may statistically be quite a small problem, even if it’s a really annoying one if it happens to you.

Fwiw,, we have seven sets of Shimano hydraulic disc brakes on various bikes and they’ve all been hassle free. Which conversely doesn’t mean there’s not a problem, just that the internet tends to amplify frustrated voices. Maybe…

Well i’ve replaced everything but the rotor and caliper on my dodgy one, and there’s a definite a lip from the spider arms to the pad contact strip. So i’ll swap the rotor and put some fresh pads in it in the near future and see how it goes.

Well, mine have never worked like that. On both bikes, as the pad gets low, the throw to biting increases (it’s slight, but enough to notice when my pads are low).

I know – I have a set that do this too – but this isn’t a “feature” of the brakes. Its an indicator of a brake not working correctly for whatever reason.

This is my understanding of how an open brake system SHOULD work….

The caliper seal acts as the spring to return the slave piston to its original starting position after you pull the brake lever. But the seal is also designed to allow the the piston to move a little bit past the seal in the event of the piston moving further than a set distance (i.e. if the lever pulls all the way to the bar).

The result of this is… if you push the pistons all the way back into the caliper and then keep pulling the brake lever, the lever will travel all the way to the bars on the first few pulls but gradually the pistons will move outwards bit by bit until the pads contact the disc. At this point the lever should be biting at the correct point in the lever stroke and the pads should remain a set distance from the disc when the brake is not applied. The size of the gap between the pads and the disc is determined by how springy the caliper seal is (i.e. how far the seal can move outwards with the piston before the piston breaks away and slips past it).

This system is designed to cope with pad wear as the pistons will move out over time to compensate for the loss of pad material while always maintaining a set distance from the disc.

As the pistons move out over time, fluid from the reservoir flows out to compensate for the increased volume of the system…but this can only happen when the lever is not being pulled. When you pull the lever past a certain point the port to the reservoir is closed off in order to allow the brake to powerfully bite down on the disc.

interesting to note the similarities between this thread and that on cable discs the other day.

Ecky-Thump – Member

JackHammer
This one?:

I only had 10 mins last night to have a look at them, but simply following the 3 step process of setting the screw mentioned in that link has all but eliminated the problem I’m having with my XTs immediately – I’ll have more time at the weekend to really look at them.

So the seal, which returns the piston also slides along the piston to account for wear? I wonder if mine are not sliding to account for this.

^^^ that’s what is generally described as a “sticky piston” alexh.
Take out the pads and cycle the pistons in and out a bit (prizing back before they come out too far and the seal pops out of the end of the bore.

It’s a good idea to clean any mud/braking dust off the piston sides before poking them back into the caliper as you’ll introduce it into the fluid otherwise. Your enemy’s toothbrush is a good tool for this.

I have this exact problem on my XT’s M8000 bought on 17/12/15. After reading this thread I’ve decided to contact the Seller CRC. Here’s a copy of my email.!!—–/

After 3 weeks of issues, regretfully i am having to email regarding a warranty issue.

I purchased the above brakes on 17/12/15, fitted a few days later I was experiencing an inconsistent brake feel, the brake bite point pumps up after initial use, especially on steep downhills, and vibrations, thinking it was the fact the rotors were not Shimano I then purchased full Shimano XT front and rear rotors from yourselves.

The initial bite point / pull of the lever is close to the bars (just how i like and set up) then subsequent quick pulls mean the next bite point is half as much away from the bar and this then returns to original pull once I’ve let off the brakes, say on the flat and then when I next pull the lever the whole things happens over again. There is no brake fade. Please note that when the yellow Blake bleed block in inserted this does not happen, the feel is perfect, it’s only when installed on a rotor.

I have since fitted the Shimano rotors and adaptors and the problem continues, I have taken the brakes and bike to my local bike shop thinking the problem was air in the system, but like me they have no air and cannot solve the inconsistent feel, they even returned my money as they were unable to help.

The bike mechanic mentioned something about there being a warranty concern regarding these model of brakes and after further inspection on the Internet and forums I can confirm that this is true. Customers are experiencing the same problem, they have also done what I have done and bled the brakes many times hoping to cure the issue but have eventually contacted their supplier r.e warranty replacement.

I have never had an issue with Shimano goods nor any product from @@@ however I’m afraid to say that these Brakes must have a warranty issue. Not only is the issue frustrating it could also be potentially dangerous.

I’m emailing this evening in the hope to ask for some help and advice and hoping that you can contact your supplier to get them exchanged. Please find a screen print of my most recent purchases.

I’m not expecting a refund for the rotors or adaptor as there is no fault with these, but please can you help with these brakes.

Another job I’ll add to the list! Thanks.

Just because no-one complains, doesn’t mean all parachutes are perfect.

My M8000s were exhibiting the same issue. Tried multiple bleeds, fiddling with the bite point etc. Earlier today I took out the wheels and gently squeezed the lever a few times until the pads moved closer together (but not too close, obviously!). Put the wheels back in, re-aligned the calipers and the problem seems to have gone. Bite point consistent with no pump up. I’m going to reserve judgement until a proper trail ride in FoD on Saturday morning though.

Are people that are having problems mainly finding that it’s the rear brake?
I’ve got a few sets of slx/xt/zee brakes. Some work perfect some not so much.
I have noticed though that all the front brakes work perfect and it’s a couple of rears I have problems with.
I plan on swapping front and rear calipers around to see where the problem goes.
Don’t think it’s a bleeding problem I’m having as i’ve bled them all the same way.

Earlier today I took out the wheels and gently squeezed the lever a few times until the pads moved closer together (but not too close, obviously!). Put the wheels back in, re-aligned the calipers and the problem seems to have gone.

I also do this and it seems good for a couple of rides them goes back to the inconsistant feel.

SSStu- Rear suggests it’s a bleeding issue. Longer, more horizontal hose line will have be trickier to eliminate air from.

Drain system and bleed bottom up – preferably off the bike with caliber vertically below the master cylinder.

Just fitted my m8000’s so will see how they go. Was hoping the new ones might be trouble free but the above reports don’t give me confidence…. 😐

Hope to produce a powerful 2 pot brake

You mean the v2…

I didn’t realise they still made those? Can’t find them on the website? Had them on a dh bike several years ago much more simple to work on the pistons than 4 pots and More powerful.

Drain system and bleed bottom up – preferably off the bike with caliber vertically below the master cylinder.

That’s what i do. Works on all but 2 of my brakes…
I know what a spongy bad bleed feels like. This is totaly different.
I’m going with the caliper piston seals causing it by pulling the pistons back in to far.
That would also explain why pumping the lever with no wheel in and closing the gap between the rotor and pads works for a short while.

I used to have this problem all the time with Formula Oro K24s. Easily solved by zip-tiing the levers back (i.e. ‘on’) to the bar in between rides.

This sorts the problem of too much lever travel for the first few braking episodes on a ride but I think the people reporting sudden brake failure mid-ride must have air in the line.

I’ve been following this thread because my back brake does exactly this. First pull, straight to the bar, then a quick extra one gets it working spot on until I release for more than a few seconds, then back to the bar again. If I do it off the bike I can see the pads going back for a few seconds after releasing the lever. I really don’t think bleeding or adding extra fluid, or using thicker discs is the solution.

singlespeedstu I think you are right, but it doesn’t explain why most people are having rear brake problems and not front. And if so why is it doing it? Would love to get to the bottom of it, I really do like thread brakes, apart from this. My wife’s are spot on.

Well my FRONT SLX does this if that helps

My M8000s were exhibiting the same issue. Tried multiple bleeds, fiddling with the bite point etc. Earlier today I took out the wheels and gently squeezed the lever a few times until the pads moved closer together (but not too close, obviously!). Put the wheels back in, re-aligned the calipers and the problem seems to have gone. Bite point consistent with no pump up. I’m going to reserve judgement until a proper trail ride in FoD on Saturday morning though.

As said above, this only improves the brake for a short while, usually about 1 ride for me. The system seems incapable of self adjusting the pads to keep a consistent bite point.

my girlfriends Kona has the problem in the rear brake, I followed the XT Tech Video on “whispers”the MBR site, and it has helped a lot, although after reading the above posts i do think there is a case for warranty replacment as it is dangerous if you are not aware of it.

as it seams to be a rear brake issue mainly, has anyone tried bleeding the brakes with the bit point adjuster / lever throw dial all the way out to try and ‘over fill’ the system? would that help?.

again, being a mainly rear caliper issue, is there any millage in better hose’s like goodridge or something similar?

This seems to happen to my brakes from time to time and, as folk have been saying, it’s also my rear one which goes.

The issue always occurs after a very wet ride at Sherwood Pines….which is odd.

So, rear brake pads wear quicker than front ones, wet rides certainly wear them down a bit. Is Sherwood pines Sandy? This does all point towards the brakes not calibrating themselves for pad wear. Either the pistons aren’t pushing past the point where they slip a bit on the seal, which I think is most likely. Or not enough extra fluid is getting pulled out of the reservoir, less likely as two quick pulls gets them working until the brake lever is released implying fluid is being pulled out of the reservoir, but then forced back in again by retracting pads

And me noticing the pads going back over the course of a few seconds could be explained by this as the seals are pulling the pistons back, but having to force the extra fluid back into the reservoir, which is going to take a bit of time, much like when you push the poisons back in to install new pads, there is always a bit of resistance.

So could it be bad quality control on the main piston seal?

Not sure if my understanding of the way they work is correct, or my descriptions make any sense, but…

So, rear brake pads wear quicker than front ones, wet rides certainly wear them down a bit. Is Sherwood pines Sandy? This does all point towards the brakes not calibrating themselves for pad wear. Either the pistons aren’t pushing past the point where they slip a bit on the seal, which I think is most likely. Or not enough extra fluid is getting pulled out of the reservoir, less likely as two quick pulls gets them working until the brake lever is released implying fluid is being pulled out of the reservoir, but then forced back in again by retracting pads

And me noticing the pads going back over the course of a few seconds could be explained by this as the seals are pulling the pistons back, but having to force the extra fluid back into the reservoir, which is going to take a bit of time, much like when you push the poisons back in to install new pads, there is always a bit of resistance.

So could it be bad quality control on the main piston seal?

I agree that this is the most likely scenario
I bled my brakes for the 3rd time in succession yesterday evening – even though I don’t believe there is air in the system – still exactly the same.

I also tried cleaning and greasing the pistons – while doing so I accidentally popped one all the way out. It seemed a little rougher than expected at the point the seal passes over it and discolored.

Does anyone know if its possible to get replacement pistons and/or seals – mine are xtr trail brakes?

I’m guessing not – this is the major advantage of Hope

You can, it just comes with a new caliper body too. 🙁

Someone on MTBR suggests that the latest XTR brakes are running the older white/cream (ceramic?) pistons. If you have ones with black pistons these are apparently known to have a (tolerance?) problem according to Shimano USA iirc.

Just as I thought 🙁
they are definately…

white/cream (ceramic?)

I don’t have Shimano brakes and have no idea why I have just read this whole thread but I’m wondering if there is a common reason why this problem occurs.
I wonder if a short set of questions could throw up a theme.

Has the front brake been bled since new?
Has the rear brake been bled since new?
What fluid was used?
What rotors are being used?
What pads are being used?
Is the problem front and rear or both?

My thoughts are that this reply from from Shimano in the article linked above if true could be an influence.

“The rubber seals in the system have to be specifically designed to interact with a specific brake fluid. If you use a different fluid, the seals will interact differently. Specifically, when you put Magura fluid in Shimano brake, the lever feels spongy and the pad contact point changes because the square edge seal at the calliper is breaking free from the piston at a different time”

Regarding the rear seeming to be more problematic it may be that some frames with internal routing etc. mean that the calliper has to come off to facilitate hose routing and consequently requires bleeding or that front cables are generally about the right length and often don’t need shortening but rears nearly always need shortening.
From experience bike shops just use car brake fluid in dot systems (even thought they often have bike branded fluid for sale on the shelf). I wonder how many use genuine Shimano mineral oil?

I wonder how many use genuine Shimano mineral oil?

I don’t have a very high regard for bike shops but Id be very surprised if any were quite daft enough to use DOT fluid….and certainly not in all of the cases mentioned in this thread.

I wasn’t saying they use dot fluid in mineral systems if you read what I said. I’m saying that I have seen them use car branded fluid in dot systems which is perfectly fine according to the manufacturers in the the article above who use dot fluid in their brakes.
I’m more posing the question of how many shops use genuine Shimano brand mineral fluid every time or do they use something cheaper?

OK but its not that as my little bottle says “Shimano” on it. Not that other mineral oil would behave any differently.

Also I use Motorcycle branded DOT fluid in my hope brakes
Why?
Cos its exactly the same and miles cheaper